Low flow analyzing from upstream to downstream in Karkheh river basin

Recognizing and analyzing the behavior of low flow indices is a prerequisite for water resource management and cropping pattern planning in arid and semi-arid regions. The purpose of this study was to analyze low flow in order to provide regional relations and identifying vulnerable areas. In this study, 26 stations with a common statistical period were selected by examining the daily stream flow data of hydrometric stations in Karkheh Basin. The daily stream flow time series was prepared for each year. Then, three, five, seven, 10, 15, 30 and 60 days low flow and average annual discharge were extracted for each year and each station. A new index was defined as the "low flow index". Then the trend detection of low flow index and its regional analysis was performed. Single and multiple regression between independent parameters of height, area, slope, distance to the outlet and related low flow indices extracted and results were analyzed. The accuracy of simulation was also estimated through the coefficient of determination. The results showed that by increasing the distance from the outlet of Karkheh basin upwards, the trend of the index was higher and in the branches, the obtained index was less than the downstream. This indicates that the branches were more vulnerable and should be focused on better water resources management in the branches.